The present invention relates to a hydraulic pump which is driven by an engine so as to generate a hydraulic pressure to be applied to a hydraulic actuating apparatus mounted to an automobile.
Recent automobiles have various hydraulic actuating apparatuses such as a power steering apparatus and automatic transmission apparatus, and a hydraulic pump for generating a hydraulic pressure to be applied to these apparatuses is mounted thereto.
Most of these hydraulic pumps utilize a part of a generated power of a car-mounted engine. These pumps are driven by a belt transmission via a power-taking-out pulley provided to an end of a crank shaft of the engine. However, in the case of such a simple transmission constitution, power loss due to the driving of the hydraulic pump is large at high-speed operation while the engine is rotating at a high speed, and thus there is a disadvantage that fuel consumption is increased. On the contrary, in the case where the specification of the hydraulic pump is determined in order to reduce this power loss, the performance of the hydraulic pump is insufficient at low-speed operation while the engine is rotating at a low speed or at stopping, and thus there arises a problem that sufficient hydraulic pressure cannot be obtained.
As mentioned above, in the hydraulic pumps which generates a hydraulic pressure to be applied to the hydraulic actuating apparatus mounted to the automobile, it is required to maintain a sufficient hydraulic pressure when necessary, and to reduce inadequate power loss of the engine as a driving source. In order to satisfy this requirement, the following two constitutions have been disclosed.
The first constitution directs its attention to, for example, that in a hydraulic-type power steering apparatus which assists a power necessary for steering by using a hydraulic pressure, most of the hydraulic actuating apparatuses mounted to automobiles do not always require the application of a hydraulic pressure, namely, the application is required only while steering. This constitution has been disclosed in Japanese Patent Application Laid-Open No. 57-15064 (1982) as a power steering apparatus, and in the apparatus, a pair of hydraulic pumps for applying a hydraulic pressure is provided, and a clutch is provided to a halfway of a transmission system of one of the hydraulic pumps and the clutch is controlled to connect/disconnect according to results of detecting a running states such as a rotational speed of the engine and steering state so that one hydraulic pump is driven normally or two hydraulic pumps are driven if necessary.
In this constitution, the reason for always driving one hydraulic pump is that a hydraulic oil is prevented from being viscous much when the air temperature is low by always providing a flow of a hydraulic oil. By capacity of the hydraulic pump always driven is made to be small, the power loss can be reduced as much as possible.
The second constitution is disclosed in Japanese Patent Application Laid-Open 7-133854 (1995), and in this constitution, a ring cone-type infinite variable-speed drive is provided between an input shaft connected with an engine and a rotor shaft of a hydraulic pump. A variable speed ring of the infinite variable-speed drive is press-moved by a pressing body which moves in the radial direction by means of a centrifugal force according to rotation of the input shaft so that a transmission ratio is changed. When the engine is rotated at a low speed, the rotation is transmitted directly to the hydraulic pump, and when the engine is rotated at a high speed, the rotation is transmitted to the hydraulic pump after the rotational speed is reduced to a predetermined value. As a result, a reduce in power loss while high-speed operation and elimination of insufficient flow of the hydraulic oil low-speed operation are achieved simultaneously.
As the infinite variable-speed drive provided between the input shaft and rotor shaft, instead of the aforementioned ring cone-type infinite variable-speed drive, another type of the infinite variable-speed drives such as the variable-speed pitch pulley-type can be used. Moreover, a change in the transmission ratio can be achieved by using an adequate actuator which is actuated according to results of detecting running states of the automobile such as a rotational speed of the engine and a steering state. The hydraulic pump having such a constitution is also suggested.
However, the first constitution requires two hydraulic pumps, transmission systems for achieving transmission between the hydraulic pumps and engine, and the clutch provided in one of the transmission systems. Further, this constitution requires a sensor for detecting the running state, and a controlling apparatus for connecting/disconnecting the clutch based on the detected results of the sensor. For this reason, the whole constitution becomes complicated, and faulty action due to external noises might occur.
Meanwhile, in the second constitution, since the transmission ratio between the input shaft and rotor shaft is changed by mechanical means actuated by means of a centrifugal force, there is an advantage that faulty actuation due to external noises might not occur. On the contrary, this constitution has a problem that the infinite variable-speed drive including the means is hardly down-sized. In the case where another infinite variable-speed drive is used instead of the ring cone-type infinite variable-speed drive in order to achieve the down-sizing, much stronger force is required to change the transmission ratio, and thus there is a problem that mechanical transmission means which is driven by the centrifugal force is hardly achieved.
In addition, in this constitution, the transmission ratio is changed only according to the rotational speed of the engine, so the actuating state of the hydraulic actuating apparatus to which hydraulic pressure is applied is not reflected. Therefore, there arose a problem that the constitution results in inadequate power loss to the engine in a running state which does not require the application of a hydraulic pressure.
This problem, as mentioned above, is eliminated by using an adequate actuator actuated according to results of detecting running states of the automobile in order to achieve the transmission. The transmission using such kind of the actuator can be achieved by using an infinite variable-speed drive other than the ring cone-type. However, in this case, similarly to the first constitution, the sensor for detecting running state and the controlling apparatus for controlling the actuator based on the detected results of the sensor are required, and thus this causes complication of the whole constitution and faulty actuation due to external noises.